The present invention relates to drill pipes for horizontal underground boring operations and to methods for making such drill pipe.
The present invention is directed first to a drill pipe comprising a tubular steel shaft with expanded ends. One end of the shaft comprises a box joint receiving portion extending from a first transitional portion which in turn extends from the shaft. The other end of the shaft comprises a pin joint receiving portion extending from a second transitional portion.
The diameter of the pin joint receiving portion and the box joint receiving portion is greater than the diameter of the tubular portion, and the diameter of each of the transitional portions expands from the diameter of the tubular portion to the diameter of the adjacent joint receiving portion. The wall thickness of the shaft is substantially the same throughout its entire length including the tubular portion, the first and second transitional portions and the joint receiving portions. The drill pipe may include a pin joint and a box joint attached to the pin joint receiving portion and the box joint receiving portion, respectively.
Still further, the present invention is directed to a method for forming a drill pipe. In accordance with this method, both ends of a length of tubular steel are expanded using a cold upsetting process. In a preferred embodiment of this method, the shaft first is stabilized. Then an internal mandrel is forced into one end of the shaft a distance equal to the portion of the end that is to be expanded so that the inner diameter of the end is enlarged. Next, an external die is applied over the end while the internal mandrel still is in place so that the end is conformed externally to the shape of the internal mandrel. The process is repeated for the other end.